Balanced bellows pressure head



April 26, 1955 c. M. HATHAWAY 2,707,001

BALANCED BELLows PRESSURE HEAD Filed March 27, 1951 United States Patent Office 05000000 Patented Apr. 26, 1955 25. The rod 2S is of a particular type of metal having a characteristic which changes its permeability in accord` 2 707 0M ance with temperature. This change of characteristic is calculated to overcome a change in permeability in tle 33A* p ED BE 'S SS E HEAD 5 remaining structure .due to temperature variations. t

LA JC LLGW PRE UR will be noted from Figure 4 that the coil 19 may be pro- Chiude M. Hathaway, Denver, Coio., assigner to Hathavided with a protective cover or disk 26, which generally way instrument Company, Denver, Colo. is of liber.

From Figures 2 and 3 it will be noted that the member Apphcan March 27 1951 Serial No' 217,766 17 at o e side is provided with cut-away ppi-tions gr a recesses 27 and 23 so that connections may e broug t J Claims' (CL IS7-785) out from the coils 19 and 21.

From Figures 1 and 3 it will be seen that on each side of the base member 17 there is provided an aperrfhe present invention relates to an electrical device for l tui-ed plate 29 and a cover plate 31, both retained in indicating pressure.

Frequently, in connection with aircraft and airborne plate 29 receives a knife edge 33 of a walking beam devices, it is desirable to have a gauge responsive to lever 34. At each end of the beam 34 there is provided pressure Which 1.11 Some Cases may be felaVelY W a set screw J5 which clamps onto one end of a spring .a6 Heretofore a pressure gauge has been employed utilizing having its other end secured to a cross plate 37. The two similar bellows connected to an electric sensing decross plate 37 is secured in position by a plurality of vice. The two bellows were arranged to be responsive screws 38. t has been found that by clamping one end to a difference of pressure existing between them. It has of the spring 36 by the set screw 3S a connection is been found, however, that a response was obtained obtained which minimizes certain hysteresis effects in the which did not correspond to the difference of pressure operation of the device. The beam 34 at intermediate between the two bellows. It was ascertained that the points also is provided with set screws 39 which engage housing for the two bellows permitted the development piano wire connections 41 leading to two similar bellows of what corresponded `to a third pressure, which thus 42 and 43. The beam 34, therefore, is engaged at its modified the response indicated by the electric sensing extremities by a plurality of springs 36 tending to hold device. the beam in a balanced position. The beam 34 is made Accordingly it is proposed, in accordance with the of iron or other magnetic material so that it, together present invention, to obviate certain disadvantages enwith the base member 17, provides complete magnetic countered in the devices of the prior art ong these paths for the electromagnetic coils 19 and 2 The coils isadvaniages is the effect of hysteresis Still another 19 and 21 together with their magnetic circuits thereeffect which is to be minimized or reduced is the variafore comprise an electric sensing device responsive to a tion which occurs when temperature changes. differential action of the bellows 42 and 43.

lt is, therefore, an object of this invention to provide The bellows 43, as may be seen from Figure 3, is conan improved pressure responsive device which will be nected to a tube 44 which may be sealed off after the more accurate than corresponding devices heretofore embellows 42 has been evacuated. The sealed off tube 44 ployed. ai) may be protected by a cover 45 This arrangement is A still further object of the invention is to provide an provided where a pressure response is to be obtained improved electric pressure head having a construction relative to absolute pressure rather than diferential presprovided to compensate for the deleterious effects of sure. The other bellows 43 is provided with a nipple 46 temperature variations. for receiving a suitable tube or conduit to receive pres- Still another object of the present invention is to pro- 45 sure to be indicated. vide an electric pressure head construction which will The bellows 43, immediately beneath the mounting minimize the effect of hysteresis. plate 12, is provided with an aperture or passage 47 so A still further object of the invention is to provide an that any pressure applied through the tube 46 to the improved electric pressure head having high sensitivity, bellows 43 is likewise applied to the interior of the casing great accuracy and aminimum of extraneous eifects. 11. The bellows 43, therefore, acts in this case as a .t uither objects and advantages of the present invenmechanical balancing device to balance out the mechanition subsequently will become apparent by reference to cal effects of the oellows 42 Each of the bellows 4" the following descriptio taken in conjunction with the and 43 is connected through a piano wire connection 41 following drawing wherein: to the beam 34 by the set screw 39, which arrangement igure 1 is a view of the present in vention wherein ,55 has been found to minimize undesired hysteresis effects a section has been taken through the casing adjacent one in the operation of the device.

side wall; Where differential pressure is to be indicated rather Figure 2 is a cross-sectional view of a portion of the than absolute pressure, the tube 44 and cap 45 of the apparatus shown in Figure 1 as seen along the line 2-2; bellows 42 is replaced by a nipple similar to the nipple igure 3 is a cross-sectional View as seen in the direc- U0 46 for the bellows 43. Such an arrangement then may be tion of the arrows along the line 3 3 of Figure l; and utilized to indicate relative or differential pressure.

Figure 4 is a cross-sectional View of a portion of the From the foregoing description it will be appreciated apparatus as seen in the direction of the arrows along that the present invention provides an improved electric the line 4 4 of Figure 2. pressure head wherein the pressure responsive devices ln the drawing there is shown a generally rectangular compiising the two bellows are mechanically balanced housing 11 having a cover 12 secured thereto by suitable and arranged in such mechanical relation as to minimize fastening means 13, The housing is made aintignt by a .the effect of hysteresis.. In one embodiment, such as that gasket 14 pour posts 15 extend downwardly from the i ustrated in the drawing, these bellows are connected to cover 12 and have reduced diameter portions 16 which in electric Sellsmg device .of the elfctm'maguec type' are hollow and threaded inside. The reduced diameter 1h03@ Sklued m the art WIH appreclate that a Structure portions extend into suitable apertures in a plate 17 of Comlfarable to the beim 3f; may be repladby Some n f othei arrangement, which will produce an electrical effect appreciable thickness, which is secured to the iour posts n proportional to the displacement between the bellows 42 y screws 1o. The plate 17 has two similar circular d 4 A d l t t l t l openings therein for receiving two coils 19 and 21. One an ny Isp amen or s ram responsive e ec nca of these coils is shown in cross section in Figure 4, from devl may be employed' ln *he resent instance, the electric sensin device co which it will be seen that a central core structure is nece Wiltjh the bellows 42 and 43 h g n tion wherein the central core of each coil is provided portion 23, which extends through an aperture iii the member 17 and is riveted therein. The rod 22 has a 80 ordinarily encountered with changes in temperature. In central or axial recess 24 into which is fitted another rod the arrangement shown, the effect is such that the sen aver/,ooi

tivity of the electric sensing device decreases as temsaid armature being pivoted at it center midway between perature increases because there is a decrease in the total said bellows, wire connections from said bellows to interpermeability of the entire magnetic circuit and an eiecmediate points on said armature, and spring means nortive increase in the air gap between the central poles of mally biasing said armature to a neutral position. each of the coils and the armature 34. 5 3. The combination comprising a sealed housing con- While for the purpose of illustrating and describing the taining a pair of bellows mounted parallel to each other present invention a preferred embodiment has been and each having passage extending to the exterior of said shown in the drawing, it is to be understood that such housing, one of said bellows having a passage in comvariations are contemplated in the components employed munication with the interior of said housing, an armaand in their arrangement as may be commensurate with 1i ture mounted with its longitudinal axis perpendicuiar to the spirit and scope of the invention set forth in the and in the same plane as the axis of said bellows, said accompanying claims. armature being pivoted at its center midway between I claim as my invention: said bellows, wire connections from said bellows to inter- 1. The combination comprising a sealed housing, a mediate points on said armature, said wire connections pair of bellows mounted parallel to each other within 13* being ciarnped to said armature, and spring means norsaid housing, each bellows having a passage extending to mally biasing said armature to a neutral position, said the exterior of said housing, one of said bellows having springs each having one end clamped to said armature, a passage in communication with the interior of said housing, a leve1 mounted so its longitudinil axis is perof) Reerences Cited in the file of this patent endicular to t e axis of said be lows an in the same 1 en; n glane thereof, said lever being pivoted at its center mid- UNULD STATED PATENTS way between said bellows, connections from said bellows 1,393,463 Lee Nov. 29, l92l to intermediate points on said lever, and spring means 1,945,375 Robbins Jan. 30, 1934 normally biasing said lever to a neutral position. v 2,659,393 Polydoroi Nov. 3, 1936 2. The combination comprising a sealed housing con 2f) 2,319,219 Draper et al May 1S, 1943 taining a pair of bellows mounted parallel to each other 2,345,464 De Giers Mar. 28, i944 and each having a passage extending to the exterior of 2,371,299 Johnson Mar. i3, 1945 said housing, one of said bellows having a passage in 2,380,242 Jewell July l0, i945 communication with the interior o said housing, an 2,460,773 Stimson Feb. l, 1949 armature mounted with its longitudinal axis perpendicu- 30 2,486,587 Callahan, Ir. et al Nov. l, i949 lar to and in the same plane as the axis of said bellows, 2,491,998 Mlkma Dec. 20, 1949 

